Sorption equilibrium and kinetics of CO₂ on clay minerals from subcritical to supercritical conditions: CO₂ sequestration at nanoscale interfaces

CO₂ sequestration in geological formations has attracted attention as a promising method to reduce anthropogenic CO₂ emission. CO₂ sorption at nanoscale interfaces of clay minerals were studied from subcritical to supercritical conditions because clay minerals are a constituent of various rocks such as a cap rock, reservoir rock and coal mineral matter. The sorption capacity and kinetics of CO₂ on montmorillonite, illite, and sepiolite were measured by a gravimetric method. Sepiolite had the highest sorption capacity at all experimental conditions. After high CO₂ pressure sorption, the desorption isotherm on montmorillonite showed significant hysteresis, but the hysteresis on illite and sepiolite was relatively weak. The excess sorption isotherms of all clay minerals showed a maximum near the critical pressure and the absolute sorption isotherms approached the saturation over the critical density value of CO₂. The surface area changes of clay minerals by supercritical CO₂ sorption were observed by comparing the N₂ sorption isotherms between the raw material and post-experiment sample. The CO₂ sorption rates on clay minerals were within a single order of magnitude (10^-8m²/s). The results at nanoscale interfaces can contribute to understanding the sorption capacity and sealing integrity of sedimentary rocks in CO₂ geological storage.